What portions of the nervous system, when stimulated, cause the constriction of blood vessels?

The stimulation of alpha-adrenergic receptors is responsible for the constriction of blood vessels, a process known as vasoconstriction. These receptors are primarily found in the smooth muscle of blood vessels, and when activated by catecholamines such as norepinephrine, they cause the muscles to contract, leading to a decrease in the diameter of the blood vessels. This response is crucial for regulating blood pressure and redirecting blood flow to vital organs during situations that require increased perfusion, such as during stress or injury.

The other choices refer to different types of receptors and their associated functions. Beta-adrenergic receptors typically mediate vasodilation, particularly in certain blood vessels like those supplying skeletal muscle and the heart, which counters the effects of alpha-adrenergic stimulation. Cholinergic receptors are primarily involved in the parasympathetic nervous system and influence functions such as reducing heart rate and promoting digestion, rather than directly causing vasoconstriction. Glucocorticoid receptors primarily engage in various metabolic processes and immune response regulation, unrelated to immediate vascular tone. Thus, the specificity of alpha-adrenergic receptor activation in facilitating blood vessel constriction is what makes this answer correct.